The present invention relates to an optical device comprising a plurality of units having at least two geometrically-differentiated tapered optical waveguides therein.
Optical waveguides, also known in the art as light transmissive devices or lightguides, find application in display devices, such as for example projection display devices, off screen display devices, and direct view displays. Typically, an optical element having a plurality of optical waveguides is used. See for example U.S. Pat. Nos. 3,218,924 and 3,279,314 to Miller and U.S. Pat. No. 4,767,186 to Bradley, Jr. et al. Such displays are used in a wide range of applications including computer terminals, airplane cockpit displays, automotive instrument panels, televisions, and other devices that provide text, graphics, or video information.
Such known displays suffer from the following problems. Depending on the exact optical waveguide geometry, known displays may produce non-monotonically decreasing light output intensity as the viewing angle is changed from normal to the optical device to parallel to the optical device. See FIG. 10 which shows the minima which occur in such a light distribution output pattern. A viewer will perceive the peaks between such lows in the light distribution output pattern as intensity hot spots, which will be clearly disadvantageous to the perception of a uniformly emissive optical device.
Another problem which occurs in known displays is the occurrence of Moire and other interference patterns. A typical liquid crystal display device has a first polarizer element, a first substrate with pixel electrodes on it and a matrix circuit section to apply voltage to these pixel electrodes, a liquid crystal layer, a second substrate having a black matrix layer with openings, and a second polarizer element. A pixel is formed by the openings on the second substrate and the pixel electrodes on the first substrate. When an optical device is assembled with such a liquid crystal display device, Moire and other inference patterns often occur because the critical dimensions for pixel pitch separation line width are similar or nearly similar to the critical dimensions for the optical device. Viewing these patterns is unappealing.
Another problem which occurs in known displays is that very specific output distributions of the light may be hard to achieve with just one type of optical waveguide present within said optical device. The output distribution of the light will be solely defined by that waveguide and thus the waveguide must be specifically designed to exactly accomodate the needs of the user.
Thus, a need exists in the art for an optical device wherein the occurrence of intensity hot spots and Moire and other interference patterns is reduced or substantially eliminated so as to provide a more uniformly emissive optical device.